Semi-persistent scheduling and discontinuous reception alignment

ABSTRACT

A method is provided for detection of an uplink grant for a user agent (UA). The method comprises detecting a semi-persistent scheduling (SPS) activation/reconfiguration signaling over a physical downlink control channel (PDCCH) only during an SPS activation window, wherein the SPS activation window precedes a discontinuous reception (DRX) on-duration by a predetermined amount of time. Also included is a UA comprising a component configured to detect an SPS activation/reconfiguration signaling over a PDCCH only during an SPS activation window, wherein the SPS activation window precedes a DRX on-duration by a predetermined amount of time.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/637,461, filed on Dec. 14, 2009, which claims priority toU.S. Provisional Patent Application No. 61/122,481, filed Dec. 15, 2008,by Yi Yu, et al, entitled “Semi-Persistent Scheduling And DiscontinuousReception Alignment” (34505-US-PRV-4214-14100), the applications areincorporated by reference herein as if reproduced in its entirety.

BACKGROUND

As used herein, the terms “user agent” and “UA” can refer to wirelessdevices such as mobile telephones, personal digital assistants, handheldor laptop computers, and similar devices that have telecommunicationscapabilities. Such a UA might consist of a wireless device and itsassociated Universal Integrated Circuit Card (UICC) that includes aSubscriber Identity Module (SIM) application, a Universal SubscriberIdentity Module (USIM) application, or a Removable User Identity Module(R-UIM) application or might consist of the device itself without such acard. The term “UA” may also refer to devices that have similar wirelesscapabilities but that are not transportable, such as telephones, desktopcomputers, set-top boxes, or network nodes. When a UA is a network node,the network node could act on behalf of another function such as awireless device and simulate or emulate the wireless device. Forexample, for some wireless devices, the IP (Internet Protocol)Multimedia Subsystem (IMS) Session Initiation Protocol (SIP) client thatwould typically reside on the device actually resides in the network andrelays SIP message information to the device using optimized protocols.In other words, some functions that were traditionally carried out by awireless device can be distributed in the form of a remote UA, where theremote UA represents the wireless device in the network. The term “UA”can also refer to any hardware or software component that can terminatea SIP session.

In traditional wireless telecommunications systems, transmissionequipment in a base station transmits signals throughout a geographicalregion known as a cell. As technology has evolved, more advanced networkaccess equipment has been introduced that can provide services that werenot possible previously. This advanced network access equipment mightinclude, for example, an enhanced node B (eNB) rather than a basestation or other systems and devices that are more highly evolved thanthe equivalent equipment in a traditional wireless telecommunicationssystem. Such advanced or next generation equipment may be referred toherein as long-term evolution (LTE) equipment, and a packet-basednetwork that uses such equipment can be referred to as an evolved packetsystem (EPS). As used herein, the term “access device” will refer to anycomponent, such as a traditional base station or an LTE eNB, that canprovide a UA with access to other components in a telecommunicationssystem.

For packet data, the signal that carries data between a UA and an accessdevice can have a specific set of frequency, time, and coding parametersand other characteristics that might be specified by the access device.A connection between a UA and an access device that has a specific setof such characteristics can be referred to as a resource. An accessdevice typically establishes a different resource for each UA with whichit is communicating at any particular time.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is an illustration of an uplink semi-persistent schedulingactivation window alignment with a discontinuous reception on-duration.

FIG. 2 is an illustration of a plurality of uplink semi-persistentscheduling activation/reconfiguration signaling detection times.

FIG. 3 is a diagram of a method for improving reliability insemi-persistent scheduling activation/reactivation according to anembodiment of the disclosure.

FIG. 4 is a diagram of a wireless communications system including a useragent operable for some of the various embodiments of the disclosure.

FIG. 5 is an illustrative general purpose computer system suitable forsome of the various embodiments of the disclosure.

DETAILED DESCRIPTION

It should be understood at the outset that although illustrativeimplementations of one or more embodiments of the present disclosure areprovided below, the disclosed systems and/or methods may be implementedusing any number of techniques, whether currently known or in existence.The disclosure should in no way be limited to the illustrativeimplementations, drawings, and techniques illustrated below, includingthe exemplary designs and implementations illustrated and describedherein, but may be modified within the scope of the appended claimsalong with their full scope of equivalents.

During a voice session between a UA and an access device, talk spurtscan alternate with silence periods. When a talk spurt ends and a silenceperiod begins on the uplink, the UA typically stops transmitting in theuplink resource that the UA had been using. On the downlink, the UAtypically stops receiving in the downlink resources that the UA has beenassigned. When the UA stops transmitting in the uplink resource, theaccess device can then grant the resource to another UA. The releasingof the resource can be initiated by the UA or by the access device. Whenthe silence period ends and a new talk spurt begins on the uplink, theUA may request that the access device grant the UA a new uplink resourceon which to resume transmitting data packets. On the downlink, theaccess device grants the UA a new downlink resource on which to resumereceiving data packets.

In a procedure known as semi-persistent scheduling (SPS) or configuredscheduling, a resource for a data packet is granted and thensubstantially the same resource is repeatedly used for subsequent datapackets. That is, in semi-persistent scheduling, the resource that anaccess device provides for data packets on an uplink or downlink isallocated at various intervals based on a grant and/or a singlescheduling request. An original grant of an SPS resource can be referredto as SPS activation. If, at a subsequent time, an access device needsto reallocate an SPS resource with different parameters, the subsequentgrant can be referred to as SPS reconfiguration.

An access device typically grants an uplink or downlink resource to a UAby sending SPS activation (or reconfiguration) signaling to the UA overthe physical downlink control channel (PDCCH). The period of time duringwhich the UA listens on the PDCCH and attempts to decode data receivedon the PDCCH can be referred to as the active time (TS 36.321). The SPSactivation/reconfiguration signaling might be only a portion of the datathat the UA typically listens for and attempts to decode during theactive time. When a UA is not in the active time, the UA may not receivethe data from the access device.

A period of time known as a discontinuous reception (DRX) on-durationcan be defined as a periodic duration during which the UA wakes up forthe purpose of monitoring the PDCCH. The length of DRX on-duration iscontrolled by an on-duration timer. A DRX cycle is a periodic repetitionof the DRX on-duration followed by a possible period of inactivity(i.e., a DRX off-duration). The DRX cycle might be defined to last for aplurality of transmission time intervals (TTIs), such as milliseconds,and the DRX on-duration might be defined to be a portion of the DRXcycle. If no other activity is going on, the UA will wake upperiodically to monitor the PDCCH for that portion of the DRX cycle andthen sleep for the remaining portion of the DRX cycle. During the DRXon-duration, the UA may be allocated the SPS uplink resource.

For instance, for an uplink assignment, the UE may detect and decode (orprocess) the transmitted SPS activation/reconfiguration signaling overthe PDCCH within a time window, referred to herein as an SPS activationwindow, which may at least partially overlap with the DRX on-duration.The SPS activation/reconfiguration signaling is detected and decodedbefore the actual uplink transmission using the activated orreconfigured uplink resource. Typically, there is some amount of time ortime delay, which may be, for example, equal to about four TTIs ormilliseconds, between the sending of the SPS activation/reconfigurationsignaling and the uplink transmission. Accordingly, the SPS activationwindow may require proper alignment to ensure the allocation of the SPSuplink grant during the DRX on-duration. A portion of the SPS activationwindow may precede the DRX on-duration by the time delay for detectingand decoding the SPS activation/reconfiguration signaling. As such, thestart of the SPS activation window may precede the start of the DRXon-duration. In one embodiment, the end of the SPS activation window mayprecede the end of the DRX on-duration by the same time delay as betweenthe start of the SPS activation window and the start of the DRXon-duration. Hence, the SPS activation/reconfiguration signaling may bedetected and decoded to allow the uplink grant to be allocated withinthe DRX on-duration.

Further, the PDCCH can include a cell radio network temporary identifier(CRNTI), an SPS RNTI, or a similar identifier, that specifies the UA forwhich the uplink resource is granted. A UA typically monitors or decodesthe PDCCH payloads throughout the active time to determine if one of thePDCCH payloads contains an identifier addressed to that UA. As usedherein, the term “payload” might refer to any formatted message. Whenthe UA decodes a PDCCH payload with the UA's identifier, the UA knowsthat the resource allocation provided in the PDCCH payload is intendedfor that UA. In some cases, a UA might receive an identifier that wasnot addressed to that UA but that the UA mistakenly identifies aspertaining to itself. The UA might then attempt to transmit data on aresource that the UA mistakenly assumes was allocated to it. Such afalse alarm or false detection can waste the UA's computing capacity andbattery power, and also cause additional uplink interference.

In an embodiment, the frequency or rate of such false alarms may bereduced or limited by limiting the length of the SPS activation window.For instance, the SPS activation window may be about equal to the DRXon-duration. Accordingly, the uplink grant allocation time may belimited between the start of the DRX on-duration and the end of the DRXon-duration. In some embodiments, the UA may stop attempting to detectand process the SPS activation/reconfiguration signaling when the uplinkresource allocated to the UA is released. In some embodiments, the UAmight begin attempting to detect and process the SPSactivation/reconfiguration signaling only after sending the accessdevice a message requesting that the access device grant an uplinkresource to the UA.

FIG. 1 illustrates an embodiment of an uplink SPS activation windowalignment with a DRX on-duration. As shown in the figure, the length ofthe SPS activation window 110 may be about equal to the length of theDRX on-duration 120. In one embodiment, the length of the SPS activationwindow 110 and similarly the length of the DRX on-duration 120 may beequal to about eight TTIs or eight milliseconds. Further, the start ofthe SPS activation window may be aligned to precede the beginning of theDRX on-duration by a sufficient amount of time for the UA to detect anddecode the SPS activation/reconfiguration signaling, and hence to allowthe UA a remaining time to transmit using the allocated uplink grantwithin the DRX on-duration. For instance, the SPSactivation/reconfiguration signaling may be aligned at about four TTIsor four milliseconds before the on duration to introduce a time delaythat may be necessary for detecting and decoding the SPSactivation/reconfiguration signaling. Accordingly, the SPSactivation/reconfiguration signaling may begin and end at about fourmilliseconds before the DRX on-duration. Thus, the actual allocation ofthe uplink grant occurs during the DRX on-duration. One skilled in theart will appreciate that the time delay is system specific and thenumbers provided herein are for example only.

FIG. 2 illustrates an embodiment of a plurality of uplink SPSactivation/reconfiguration signaling detection times. In an embodiment,when DRX is implemented, an access device may transmit, over the PDCCH,the uplink SPS activation/reconfiguration signaling within an SPSactivation window 110 preceding each DRX on-duration 120 by about thesame amount of time (e.g. four TTIs). This is typically done at thebeginning of a talk spurt for activation or during a talk spurt forreconfiguration. Since the access device transmits the SPSactivation/reconfiguration signaling during the SPS activation window110, it is not necessary for the UA to try to detect SPSactivation/reconfiguration signaling outside of the SPS activationwindow 110. By limiting the detection time for SPSactivation/reconfiguration signaling to only the SPS activation window110, the false alarm probability for SPS activation may be reduced.Otherwise, if the UA detects the SPS activation/reconfiguration signalwithout time limitation or during a longer time window, the UA maymistakenly identify more resources as being allocated and use suchresources to transmit data. Consequently, the amount of false alarms canincrease and the UA can waste battery power. Furthermore, this falsedetection of the SPS allocation would cause additional interference inthe system.

FIG. 3 illustrates an embodiment of a method 400 for improvingreliability in the detection of an identifier for a UA during an uplinkactivation procedure. At block 410, the UA attempts to decode the uplinkSPS activation/reconfiguration signaling only during an SPS activationwindow. In this embodiment, the start of the SPS activation window mayprecede the start of the DRX on-duration by a predetermined time delay,such as four milliseconds (or TTIs). In some cases, the UA might stopattempting to decode the uplink SPS activation/reconfiguration signalingwhen the resource that the UA is using to communicate with an accessdevice is released. In some cases, the UA might have begun attempting todecode the uplink SPS activation/reconfiguration signaling when the UAsent the access device a buffer status report or a voice packet.

FIG. 4 illustrates a wireless communications system including anembodiment of a UA 510. The UA 510 is operable for implementing aspectsof the disclosure, but the disclosure should not be limited to theseimplementations. Though illustrated as a mobile phone, the UA 510 maytake various forms including a wireless handset, a pager, a personaldigital assistant (PDA), a portable computer, a tablet computer, or alaptop computer. Many suitable devices combine some or all of thesefunctions. In some embodiments of the disclosure, the UA 510 is not ageneral purpose computing device like a portable, laptop or tabletcomputer, but rather is a special-purpose communications device such asa mobile phone, a wireless handset, a pager, a PDA, or atelecommunications device installed in a vehicle. In another embodiment,the UA 510 may be a portable, laptop or other computing device. The UA510 may also be a device, include a device, or be included in a devicethat has similar capabilities but that is not transportable, such as afixed line telephone, a desktop computer, a set-top box, or a networknode. The UA 510 may support specialized activities such as gaming,inventory control, job control, and/or task management functions, and soon.

The UA 510 includes a display 502. The UA 510 also includes atouch-sensitive surface, a keyboard or other input keys generallyreferred as 504 for input by a user. Among the various applicationsexecutable by the UA 510 are a web browser, which enables the display502 to show a web page. The web page may be obtained via wirelesscommunications with a wireless network access node, a cell tower, a peerUA 510, or any other wireless communication network or system 500. Thenetwork 500 is coupled to a wired network 508, such as the Internet. Viathe wireless link and the wired network, the UA 510 has access toinformation on various servers, such as a server 520. The server 520 mayprovide content that may be shown on the display 502. Alternately, theUA 510 may access the network 500 through a peer UA 510 acting as anintermediary, in a relay type or hop type of connection.

The UA 510 and other components described above might include aprocessing component that is capable of executing instructions relatedto the actions described above. FIG. 5 illustrates an example of asystem 600 that includes a processing component 610 suitable forimplementing one or more embodiments disclosed herein. In addition tothe processor 610 (which may be referred to as a central processor unitor CPU), the system 600 might include network connectivity devices 620,random access memory (RAM) 630, read only memory (ROM) 640, secondarystorage 650, and input/output (I/O) devices 660. These components mightcommunicate with one another via a bus 670. In some cases, some of thesecomponents may not be present or may be combined in various combinationswith one another or with other components not shown. These componentsmight be located in a single physical entity or in more than onephysical entity. Any actions described herein as being taken by theprocessor 610 might be taken by the processor 610 alone or by theprocessor 610 in conjunction with one or more components shown or notshown in the drawing, such as a digital signal processor (DSP).

The processor 610 executes instructions, codes, computer programs, orscripts that it might access from the network connectivity devices 620,RAM 630, ROM 640, or secondary storage 650 (which might include variousdisk-based systems such as hard disk, floppy disk, or optical disk).While only one CPU 610 is shown, multiple processors may be present.Thus, while instructions may be discussed as being executed by aprocessor, the instructions may be executed simultaneously, serially, orotherwise by one or multiple processors. The processor 610 may beimplemented as one or more CPU chips.

The network connectivity devices 620 may take the form of modems, modembanks, Ethernet devices, universal serial bus (USB) interface devices,serial interfaces, token ring devices, fiber distributed data interface(FDDI) devices, wireless local area network (WLAN) devices, radiotransceiver devices such as code division multiple access (CDMA)devices, global system for mobile communications (GSM) radio transceiverdevices, worldwide interoperability for microwave access (WiMAX)devices, and/or other well-known devices for connecting to networks.These network connectivity devices 620 may enable the processor 610 tocommunicate with the Internet or one or more telecommunications networksor other networks from which the processor 610 might receive informationor to which the processor 610 might output information. The networkconnectivity devices 620 might also include one or more transceivercomponents 625 capable of transmitting and/or receiving data wirelessly.

The RAM 630 might be used to store volatile data and perhaps to storeinstructions that are executed by the processor 610. The ROM 640 is anon-volatile memory device that typically has a smaller memory capacitythan the memory capacity of the secondary storage 650. ROM 640 might beused to store instructions and perhaps data that are read duringexecution of the instructions. Access to both RAM 630 and ROM 640 istypically faster than to secondary storage 650. The secondary storage650 is typically comprised of one or more disk drives or tape drives andmight be used for non-volatile storage of data or as an over-flow datastorage device if RAM 630 is not large enough to hold all working data.Secondary storage 650 may be used to store programs that are loaded intoRAM 630 when such programs are selected for execution.

The I/O devices 660 may include liquid crystal displays (LCDs), touchscreen displays, keyboards, keypads, switches, dials, mice, track balls,voice recognizers, card readers, paper tape readers, printers, videomonitors, or other well-known input or output devices. Also, thetransceiver 625 might be considered to be a component of the I/O devices660 instead of or in addition to being a component of the networkconnectivity devices 620. Some or all of the I/O devices 660 may besubstantially similar to various components depicted in the previouslydescribed drawing of the UA 510, such as the display 502 and the input504.

The following 3rd Generation Partnership Project (3GPP) TechnicalSpecification (TS) is incorporated herein by reference: TS 36.321.

According to one embodiment, a method for detection of an uplink grantfor a UA. The method comprises detecting an SPSactivation/reconfiguration signaling over a PDCCH only during an SPSactivation window, wherein the SPS activation window precedes a DRXon-duration by a predetermined amount of time.

In another embodiment, a method is provided for detection of an uplinkgrant for a UA. The method comprises transmitting an SPSactivation/reconfiguration signaling over a PDCCH only during an SPSactivation window, wherein the SPS activation window precedes a DRXon-duration by a predetermined amount of time.

In another embodiment, a user agent is provided. The user agentcomprises a component configured to detect an SPSactivation/reconfiguration signaling over a PDCCH only during an SPSactivation window, wherein the SPS activation window precedes a DRXon-duration by a predetermined amount of time.

In another embodiment, an access equipment is provided. The accessequipment comprises a component configured to transmit an SPSactivation/reconfiguration signaling over a PDCCH only during an SPSactivation window, wherein the SPS activation window precedes a DRXon-duration by a predetermined amount of time.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

Also, techniques, systems, subsystems and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component, whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method in a user equipment that operates inaccordance with a configured discontinuous reception (DRX) cycle inwhich the user equipment monitors a physical downlink control channel(PDCCH) during at least a defined DRX on-duration of the configured DRXcycle, the method comprising: sending to an access device a request foran uplink transmission resource; and monitoring the PDCCH forsemi-persistent scheduling (SPS) activation signaling associated with agrant of an SPS resource after sending the request, wherein saidmonitoring occurs during a time period that at least partially precedesa start of the defined DRX on-duration.
 2. The method of claim 1,wherein said monitoring the PDCCH for SPS activation signaling occursprior to the start of the defined DRX on-duration regardless of theconfigured DRX cycle.
 3. The method of claim 1, wherein the operation ofsending the request for the uplink transmission resource occurs prior tothe start of the defined DRX on-duration.
 4. The method of claim 1,further comprising refraining from monitoring the PDCCH for SPSactivation signaling until after the request is transmitted.
 5. Themethod of claim 1, wherein sending the request includes transmitting amessage to the access device requesting the uplink transmission resourceprior to the start of the defined DRX on-duration of the configured DRXcycle.
 6. The method of claim 5, wherein the request for the uplinktransmission resource occurs as a result of a talk spurt after a silenceperiod in a voice session.
 7. The method of claim 1, wherein saidmonitoring includes detecting and decoding SPS activation signalingreceived via the PDCCH.
 8. The method of claim 7, wherein detecting anddecoding occurs only during an SPS activation window, the SPS activationwindow that at least partially precedes the start of the defined DRXon-duration.
 9. The method of claim 8, wherein the SPS activation windowprecedes the start of the defined DRX on-duration by a predeterminedamount of time.
 10. The method of claim 8, wherein the SPS activationwindow is limited to a predetermined duration that is associated withthe defined DRX on-duration.
 11. The method of claim 8, wherein the SPSactivation window ends when the uplink transmission resource isreleased.
 12. A user equipment (UE) that operates in accordance with aconfigured discontinuous reception (DRX) cycle in which the userequipment monitors a physical downlink control channel (PDCCH) during adefined DRX on-duration of the configured DRX cycle, the user equipmentcomprising: a processor configured to send to an access device a requestfor an uplink transmission resource; and the processor furtherconfigured to monitor the PDCCH for semi-persistent scheduling (SPS)activation signaling associated with a grant of an SPS resource aftersending the request and during a time period that at least partiallyprecedes a start of the defined DRX on-duration.
 13. The user equipmentof claim 12, wherein the processor is configured to monitor the PDCCHfor SPS activation signaling prior to the start of the defined DRXon-duration regardless of the configured DRX cycle.
 14. The userequipment of claim 12, wherein the processor is configured to send therequest for the uplink transmission resource occurs prior to the startof the defined DRX on-duration.
 15. The user equipment of claim 12,wherein the processor is further configured to refrain from monitoringthe PDCCH for SPS activation signaling until after the request istransmitted.
 16. The user equipment of claim 12, wherein the processorbeing configured to send the request includes the processor configuredto transmit a message to the access device requesting the uplinktransmission resource prior to the start of the defined DRX on-durationof the configured DRX cycle.
 17. The user equipment of claim 16, whereinthe request for the uplink transmission resource occurs as a result of atalk spurt after a silence period in a voice session.
 18. The userequipment of claim 12, wherein the processor configured to monitorincludes the processor being configured to detect and decode SPSactivation signaling received via the PDCCH.
 19. The user equipment ofclaim 18, wherein the processor is configured to detect and decode onlyduring an SPS activation window, the SPS activation window that at leastpartially precedes the start of the defined DRX on-duration.
 20. Theuser equipment of claim 19, wherein the SPS activation window precedesthe start of the defined DRX on-duration by a predetermined amount oftime.
 21. The user equipment of claim 19, wherein the SPS activationwindow is limited to a predetermined duration that is associated withthe defined DRX on-duration.
 22. A non-transitory computer-readablemedium having computer executable instructions stored thereon forimplementing a method in a user equipment that operates in accordancewith a configured discontinuous reception (DRX) cycle in which the userequipment monitors a physical downlink control channel (PDCCH) during atleast a defined DRX on-duration of the configured DRX cycle, theinstructions comprising: sending to an access device a request for anuplink transmission resource; and monitoring the PDCCH forsemi-persistent scheduling (SPS) activation signaling associated with agrant of an SPS resource after sending the request, wherein saidmonitoring occurs during a time period that at least partially precedesa start of the defined DRX on-duration.
 23. The computer-readable mediumof claim 22, wherein said monitoring the PDCCH for SPS activationsignaling occurs prior to the start of the defined DRX on-durationregardless of the configured DRX cycle.
 24. The computer-readable mediumof claim 22, wherein the operation of sending the request for the uplinktransmission resource occurs prior to the start of the defined DRXon-duration.
 25. The computer-readable medium of claim 22, furthercomprising refraining from monitoring the PDCCH for SPS activationsignaling until after the request is transmitted.
 26. Thecomputer-readable medium of claim 22, wherein sending the requestincludes transmitting a message to the access device requesting theuplink transmission resource prior to the start of the defined DRXon-duration of the configured DRX cycle.
 27. The computer-readablemedium of claim 26, wherein the request for the uplink transmissionresource occurs as a result of a talk spurt after a silence period in avoice session.
 28. The computer-readable medium of claim 22, whereinsaid monitoring includes detecting and decoding SPS activation signalingreceived via the PDCCH.
 29. The computer-readable medium of claim 28,wherein detecting and decoding occurs only during an SPS activationwindow, the SPS activation window that at least partially precedes thestart of the defined DRX on-duration.
 30. The computer-readable mediumof claim 29, wherein the SPS activation window precedes the start of thedefined DRX on-duration by a predetermined amount of time.